Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    The potential of highly nutritious frozen stages of Tyrophagus putrescentiae as a supplemental food source for the predatory mite Amblyseius swirskii
    Pirayeshfar, Fatemeh ; Safavi, Seyed Ali ; Sarraf Moayeri, Hamid Reza ; Messelink, Gerben J. - \ 2020
    Biocontrol Science and Technology 30 (2020)5. - ISSN 0958-3157 - p. 403 - 417.
    astigmatid mites - biological control - frozen hosts - phytoseiidae - western flower thrips

    Astigmatid mites have potential as supplementary prey items to support generalist predator populations in crops. However, applying living prey mites has some disadvantages; if not predated they have the potential to cause crop damage and allergies. In this study, we evaluated various diets based on the astigmatid mite Tyrophagous putrescentiae (Schrank) as a supplemental food source for the predatory mite Amblyseius swirskii Ahias-Henriot. Eggs and larvae of T. putrescentiae were reared on a diet of dog food (rich in proteins and fat) or bran (rich in carbohydrate); they were offered either frozen or alive, and either with or without cattail pollen (Typha angustifolia L.). Oviposition rate of A. swirskii fed with frozen mite larvae reared on dog food was similar to the rate observed when they were fed with cattail pollen or living prey mites, but developmental time of A. swirskii was longer on this frozen diet than on a diet of living prey mites or pollen. Both living and frozen prey mites were, in contrast with cattail pollen, not suitable for oviposition by western flower thrips, Frankliniella occidentalis Pergande. In a greenhouse study, the use of frozen prey mite stages as supplemental food on chrysanthemum plants allowed populations of A. swirskii to establish, but not increase; in contrast, provision of living prey mites and pollen increased A. swirskii populations on plants. Hence, our study shows that living prey mites, but not frozen prey mites, had the greatest potential as a supplemental food source for A. swirskii.

    Supplemental food that supports both predator and pest: A risk for biological control?
    Leman, A. ; Messelink, G.J. - \ 2015
    Experimental and Applied Acarology 65 (2015)4. - ISSN 0168-8162 - p. 511 - 524.
    neoseiulus-cucumeris acari - mite amblyseius-swirskii - western flower thrips - orius-laevigatus - apparent competition - factitious foods - life-history - prey - phytoseiidae - pollen
    Supplemental food sources to support natural enemies in crops are increasingly being tested and used. This is particularly interesting for generalist predators that can reproduce on these food sources. However, a potential risk for pest control could occur when herbivores also benefit from supplemental food sources. In order to optimize biological control, it may be important to select food sources that support predator populations more than herbivore populations. In this study we evaluated the nutritional quality of four types of supplemental food for the generalist predatory mites Amblyseius swirskii Athias-Henriot and Amblydromalus (Typhlodromalus) limonicus (Garman and McGregor), both important thrips predators, and for the herbivore western flower thrips Frankliniella occidentalis Pergande, by assessing oviposition rates. These tests showed that application of corn pollen, cattail pollen or sterilized eggs of Ephestia kuehniella Zeller to chrysanthemum leaves resulted in three times higher oviposition rates of thrips compared to leaves without additional food. None of the tested food sources promoted predatory mites or western flower thrips exclusively. Decapsulated cysts of Artemia franciscana Kellogg were not suitable, whereas cattail pollen was very suitable for both predatory mites and western flower thrips. In addition, we found that the rate of thrips predation by A. swirskii can be reduced by 50 %, when pollen is present. Nevertheless, application of pollen or Ephestia eggs to a chrysanthemum crop still strongly enhanced the biological control of thrips with A. swirskii, both at low and high release densities of predatory mites through the strong numerical response of the predators. Despite these positive results, application in a crop should be approached with caution, as the results may strongly depend on the initial predator–prey ratio, the nutritional quality of the supplemental food source, the species of predatory mites, the distribution of the food in the crop and the type of crop.
    Basiskennis roofmijten voor een betere plaagbestrijding : literatuurstudie naar de effecten van gewas, klimaat en licht op generalistische bladbewonende roofmijten
    Messelink, G.J. ; Holstein, R. van - \ 2012
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport / Wageningen UR Glastuinbouw ) - 12
    biologische bestrijding - organismen ingezet bij biologische bestrijding - roofmijten - phytoseiidae - plagenbestrijding - glastuinbouw - natuurlijke vijanden - trialeurodes vaporariorum - frankliniella occidentalis - kasgewassen - klimaat - belichting - biological control - biological control agents - predatory mites - phytoseiidae - pest control - greenhouse horticulture - natural enemies - trialeurodes vaporariorum - frankliniella occidentalis - greenhouse crops - climate - illumination
    Doel van dit project is om de belangrijkste basiseigenschappen van generalistische roofmijten in kaart te brengen, om daarmee een beter advies te kunnen geven over de inzet van roofmijten in o.a. de teelt van potplanten. Gestart wordt met een literatuurstudie gevolgd door laboratoriumtesten met 6 soorten roofmijten. Deze publicatie beschrijft de literatuurstudie.
    Roofmijten tegen trips in roos
    Pijnakker, J. ; Leman, A. - \ 2012
    Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1201) - 30
    rozen - rosaceae - insectenplagen - thrips - roofmijten - roofinsecten - anthocoridae - phytoseiidae - biologische bestrijding - verbetering - glastuinbouw - nederland - roses - rosaceae - insect pests - thrips - predatory mites - predatory insects - anthocoridae - phytoseiidae - biological control - improvement - greenhouse horticulture - netherlands
    De californische trips Frankliniella occidentalis (Pergande) van de familie van de Thripidae komt oorspronkelijk uit de westkust van Californië (Bryan & Smith, 1956). Haar introductie in Europa dateert van 1984. In de glastuinbouw is californische trips, één van de belangrijkste plagen. Ze vormt het belangrijkste struikelblok voor de verdere uitbreiding van geïntegreerde bestrijding. In roos kan slechts een kleine aantal tripsen belangrijke schade veroorzaken. Veel telers hanteren bij een wekelijkse telling een aantal van 10 tripsen op een blauwe signaalplaat als schadedrempel. Tripsen zijn moeilijk te bestrijden omdat ze zich in het gewas verschuilen en resistent zijn tegen veel insecticiden. De meest gebruikte chemische tripsmiddelen zijn Match (lufenuron), Conserve (spinosad), Vertimec (abamectine), Actara (thiamethoxam) en Mesurol (methiocarb). De laatste 10 jaren heeft geïntegreerde bestrijding zich in roos enorm ontwikkeld. In 2012 introduceert meer dan 70% van de rozentelers roofmijten tegen spint en/of trips en/of kaswittevlieg. In 2002 paste slechts 15% van de Nederlandse rozentelers jaarrond geïntegreerde gewasbescherming toe. Voor het gewas roos is een reeks roofmijtensoorten geschikt gebleken uit onderzoek in voorafgaande projecten. Het project heeft als doel de beste strategie te vinden voor de rozenteelt en met voorkeur voor een roofmijtensoort met affiniteit voor roos (vestiging).
    Whether ideal free or not, predatory mites distribute so as to maximize reproduction
    Hammen, T. van der; Montserrat, M. ; Sabelis, M.W. ; Roos, A.M. ; Janssen, A. - \ 2012
    Oecologia 169 (2012)1. - ISSN 0029-8549 - p. 95 - 104.
    free distribution models - unequal competitors - egg predation - interference - density - prey - phytoseiidae - oviposition - tests
    Ideal free distribution (IFD) models predict that animals distribute themselves such that no individual can increase its fitness by moving to another patch. Many empirical tests assume that the interference among animals is independent of density and do not quantify the effects of density on fitness traits. Using two species of predatory mites, we measured oviposition as a function of conspecific density. Subsequently, we used these functions to calculate expected distributions on two connected patches. We performed an experimental test of the distributions of mites on two such connected patches, among which one had a food accessibility rate that was twice as high as on the other. For one of the two species, Iphiseius degenerans, the distribution matched the expected distribution. The distribution also coincided with the ratio of food accessibility. The other species, Neoseiulus cucumeris, distributed itself differently than expected. However, the oviposition rates of both species did not differ significantly from the expected oviposition rates based on experiments on single patches. This suggests that the oviposition rate of N. cucumeris was not negatively affected by the observed distribution, despite the fact that N. cucumeris did not match the predicted distributions. Thus, the distribution of one mite species, I. degenerans, was in agreement with IFD theory, whereas for the other mite species, N. cucumeris, unknown factors may have influenced the distribution of the mites. We conclude that density-dependent fitness traits provide essential information for explaining animal distributions
    Geïntegreerde bestrijding van trips in roos: Evaluatie van nieuwe roofmijten
    Pijnakker, J. ; Leman, A. - \ 2011
    Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1078) - 45
    insectenplagen - thrips - phytoseiidae - geïntegreerde bestrijding - rozen - rosaceae - teelt onder bescherming - bloementeelt - literatuuroverzichten - roofmijten - nieuwe soorten - inventarisaties - biologische bestrijding - droogteresistentie - gewasbescherming - insect pests - thrips - phytoseiidae - integrated control - roses - rosaceae - protected cultivation - floriculture - literature reviews - predatory mites - new species - inventories - biological control - drought resistance - plant protection
    Abstract Predatory bugs (Anthocorids) and predatory mites (Phytoseiids) are the most effective beneficials against thrips. If predatory bugs have low affinity to the rose crop, there is a series of predatory mites which is suitable for this crop, including Amblyseius swirskii, Euseius ovalis, Typhlodromalus limonicus, Amblyseius degenerans, Amblyseius andersoni and Amblyseius aurescens. The low humidity in the leaf microclimate by prolonged periods of heat can be a limiting factor. Therefore, drought-resistant mites (‘desert species’) were selected in this study and tested for their affinity for thrips and roses. Euseius stipulatus and Typhlodromus exhilaratus were found to be drought-resistant species and to predate on thrips. Euseius stipulatus settled on roses. Due to a shortage of rearing, the affinity of Typhlodromus exhilaratus for roses was not tested.
    The presence of webbing affects the oviposition rate of two-spotted spider mites, Tetranychus urticae (Acari: Tetranychidae)
    Oku, K. ; Magalhães, S. ; Dicke, M. - \ 2009
    Experimental and Applied Acarology 49 (2009)3. - ISSN 0168-8162 - p. 167 - 172.
    womersleyi schicha acari - predatory mite - spinning behavior - phytophagous mite - plant - phytoseiidae - aggregation - kanzawai - eggs - avoidance
    Several species of tetranychid mites including Tetranychus urticae Koch (Acari: Tetranychidae) construct complicated three-dimensional webs on plant leaves. These webs provide protection against biotic and abiotic stress. As producing web is likely to entail a cost, mites that arrive on a leaf with web are expected to refrain from producing it, because they will gain the benefit of protection from the existing web. Mites that produce less web may then allocate resources that are not spent on web construction to other fitness-enhancing activities, such as laying eggs. To test this, the oviposition rate of T. urticae adult females was examined on leaves with web. As a control, we used leaves where the web had been removed, hence both types of leaves had been exposed to conspecifics previously and were thus damaged. On leaves with web, the oviposition rate of T. urticae females was higher than on leaves where the web had been removed. Therefore, the presence of web constructed by conspecifics enhanced the oviposition rate of T. urticae females. This provides indirect evidence that mites use the web constructed by conspecifics and thereby save resources that can be allocated to other traits that enhance reproductive success
    Rovers ontmaskerd via hun DNA-profiel : Moleculaire identificatie van roofmijten van de familie Phytoseiidae
    Ramakers, P.M.J. ; Linden, A. van der; Pham, K.T.K. - \ 2009
    Onder Glas 6 (2009)3. - p. 12 - 13.
    kassen - kasgewassen - roofmijten - dna - uitzettingstechnieken - natuurlijke vijanden - phytoseiidae - identificatie - glastuinbouw - moleculaire merkers - glasgroenten - groenten - greenhouses - greenhouse crops - predatory mites - dna - release techniques - natural enemies - phytoseiidae - identification - greenhouse horticulture - molecular markers - greenhouse vegetables - vegetables
    In kasgewassen treffen we in toenemende mate roofmijten aan, geïntroduceerd of spontaan optredend. Voor het microscopisch determineren hiervan bestaan identificatiesleutels, gedrukte exemplaren, maar tegenwoordig ook digitaal. Deze zijn echter alleen hanteerbaar voor ervaren specialisten. Om hun werk te verlichten construeerde PPO Lisse moleculaire markers voor de belangrijkste roofmijtsoorten
    Comparison of thread-cutting behaviour in three specialist predatory mites to cope with complex webs of Tetranychus spider mites
    Shimoda, T. ; Kishimoto, H. ; Takabayashi, J. ; Amano, H. ; Dicke, M. - \ 2009
    Experimental and Applied Acarology 47 (2009)2. - ISSN 0168-8162 - p. 111 - 120.
    insect predator - natural enemies - phytoseiidae - acari - prey - thysanoptera - thripidae - success - stage
    Anti-predator defenses provided by complex webs of Tetranychus mites can severely impede the performance of generalist predatory mites, whereas this may not be true for specialist predatory mites. Although some specialist predatory mites have developed morphological protection to reduce the adverse effects of complex webs, little is known about their behavioral abilities to cope with the webs. In this study, we compared thread-cutting behavior of three specialist predatory mites, Phytoseiulus persimilis, Neoseiulus womersleyi and N. californicus, exhibited inside the complex web of T. urticae. No major difference was observed among them in the basic pattern of this behavior, using chelicerae and palps, and in the number of silken threads severed while moving inside the web. These results and observations suggest that each predator species cut many sticky silken threads to move inside the complex web without suffering from serious obstruction
    Role of excreta in predator avoidance by the Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae)
    Oku, K. - \ 2008
    European Journal of Entomology 105 (2008)4. - ISSN 1210-5759 - p. 619 - 623.
    enemy-free space - womersleyi schicha acari - host-plant acceptance - phytophagous mite - kishida acari - urticae acari - refuge - prey - phytoseiidae - behavior
    The Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae) constructs webs over leaf surfaces and usually lives under these webs. T. kanzawai produces two types of excreta, black and yellow pellets, and uses its webs as a place for excretion. T. kanzawai also uses its webs as a refuge when the predatory mite, Neoseiulus womersleyi (Acari: Phytoseiidae) is present. To clarify what factors deter N. womersleyi from foraging on T. kanzawai webs, I experimentally examined the effects of T. kanzawai excreta on its own fitness (fecundity) and the foraging behaviour of N. womersleyi. When the excreta of T. kanzawai was put on leaf surfaces, the fecundity of T. kanzawai adult females was reduced by the black but not the yellow faecal pellets. On the other hand, predation by N. womersleyi was reduced by the yellow but not the black pellets. Although this effect of the yellow pellets on N. womersleyi did not last on leaf surfaces, it deterred N. womersleyi from staying on the web regardless of its freshness. These results suggest that T. kanzawai deposits black pellets on webs to avoid its negative effect on their own fitness, and yellow pellets are deposited on webs to reduce the risk of predation.
    Biologische bestrijding met potplanten
    Messelink, Gerben - \ 2007
    biological control - pot plants - pot culture - predatory mites - phytoseiidae - substrates - greenhouses - trials - biological control agents - scientific research - greenhouse horticulture
    Entomofauna van Noordoost-Twente verslag van de 158e zomerbijeenkomst te Ootmarsum
    Cuppen, J.G.M. ; Vorst, O.F.J. - \ 2004
    Entomologische Berichten 64 (2004)6. - ISSN 0013-8827 - p. 188 - 208.
    entomologie - inventarisaties - insecten - geleedpotigen - anthoseius - phytoseiidae - typhlodromus - coleoptera - roofmijten - twente - overijssel - entomology - inventories - insects - arthropods - anthoseius - phytoseiidae - typhlodromus - coleoptera - predatory mites - twente - overijssel
    De 158e zomerbijeenkomst van de NEV vond plaats van 13 tot 15 juni 2003 in de provincie Overijssel in de omgeving van Ootmarsum. Deze bijdrage vormt de neerslag van de inventarisatieactiviteiten die door de deelnemers aan dit weekend werden ontplooid. Er werden 1484 taxa geregistreerd behorend tot negentien verschillende ordes van geleedpotigen. Met 744 taxa namen de kevers ongeveer de helft van de soorten voor hun rekening. Het aantal nieuwe soorten voor de provincie Overijssel was beperkt. Hoewel Overijssel van oudsher een relatief goed onderzochte provincie is, leverde de uitgebreide terreininventarisaties een schat aan (deels nieuwe) entomologische gegevens op. De roofmijten Anthoseius piceae en Typhlodromus bichaetae werden voor het eerst in Nederland waargenomen
    Exposure of Lima bean leaves to volatiles from herbivore-induced conspecific plants results in emission of carnivore attractants: active or passive process?
    Choh, Y. ; Shimoda, T. ; Ozawa, R. ; Dicke, M. ; Takabayashi, J. - \ 2004
    Journal of Chemical Ecology 30 (2004)7. - ISSN 0098-0331 - p. 1305 - 1317.
    tetranychus-urticae - field conditions - natural enemies - jasmonic acid - spider-mites - attack - phytoseiidae - responses - mutualism - predator
    There is increasing evidence that volatiles emitted by herbivore-damaged plants can cause responses in downwind undamaged neighboring plants, such as the attraction of carnivorous enemies of herbivores. One of the open questions is whether this involves an active (production of volatiles) or passive (adsorption of volatiles) response of the uninfested downwind plant. This issue is addressed in the present study. Uninfested lima bean leaves that were exposed to volatiles from conspecific leaves infested with the spider mite Tetranychus urticae, emitted very similar blends of volatiles to those emitted from infested leaves themselves. Treating leaves with a protein-synthesis inhibitor prior to infesting them with spider mites completely suppressed the production of herbivore-induced volatiles in the infested leaves. Conversely, inhibitor treatment to uninfested leaves prior to exposure to volatiles from infested leaves did not affect the emission of volatiles from the exposed, uninfested leaves. This evidence supports the hypothesis that response of the exposed downwind plant is passive. T. urticae-infested leaves that had been previously exposed to volatiles from infested leaves emitted more herbivore-induced volatiles than T. urticae-infested leaves previously exposed to volatiles from uninfested leaves. The former leaves were also more attractive to the predatory mite, Phytoseiulus persimilis, than the latter. This shows that previous exposure of plants to volatiles from herbivore-infested neighbors results in a stronger response of plants in terms of predator attraction when herbivores damage the plant. This supports the hypothesis that the downwind uninfested plant is actively involved. Both adsorption and production of volatiles can mediate the attraction of carnivorous mites to plants that have been exposed to volatiles from infested neighbors.
    Life history characteristics of Frankliniella occidentalis on cucumber leaves with and without supplemental food
    Hulshof, J. ; Ketoja, E. ; Vänninen, I. - \ 2003
    Entomologia Experimentalis et Applicata 108 (2003). - ISSN 0013-8703 - p. 19 - 32.
    flower thrips thysanoptera - resistant cucumber - pollen - phytoseiidae - populations - tables - models - acari - plant - mites
    The development time, fecundity, longevity, and resultant intrinsic growth rate of the western flower thrips Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae] encaged on a cucumber leaf were compared among seven types of food supplied: six pollen species and a mixture of milk powder and yeast. The rationale was to find a food source that offers the least benefit for thrips and could therefore be considered as a food source for the preventative introduction of thrips predators. With the exception of the mixture of milk powder and yeast, all the food sources tested offered a nutritional benefit for the thrips. The addition of pollen increased fecundity and reduced development time, mainly during the larval stage. Betula pubescens and Corylus avellana pollen also increased adult longevity. The nutritional benefit of Pinus sylvestris pollen was greater than that of the other five pollen species, as manifested by its significantly greater positive effect on fecundity. The other pollen species could not be ranked in terms of nutritional benefit to F. occidentalis. The negative effect of the milk powder plus yeast mix on the life-table parameters of F. occidentalis probably only occurs in an encaged situation where thrips cannot escape from the unfavorable environment. The crude estimate of the intrinsic growth rate of F. occidentalis increased from 0.163 on the plain cucumber leaf to 0.240 when P. sylvestris pollen was added to the leaf. The differences in intrinsic growth rate mainly reflect the differences in fecundity among the food sources. Thus, the peak oviposition rate may be used as a measure of the nutritional benefit F. occidentalis can obtain by feeding on supplemental food sources. The positive effect of a supplemental food source on thrips does not necessarily mean it is unsuitable for the preventative introduction of thrips predators, because the supplemental food can also affect the population dynamics of the predator and the predator-prey interaction and, hence, the outcome of biological control.
    Differences among plant species in acceptance by the spider mite Tetranychus urticae Koch
    Boom, C.E.M. van den; Beek, T.A. van; Dicke, M. - \ 2003
    Journal of Applied Entomology 127 (2003)3. - ISSN 0931-2048 - p. 177 - 183.
    phytophagous mite - manduca-sexta - host - acari - resistance - phytoseiidae - lepidoptera - population - induction - selection
    The spider mite Tetranychus urticae Koch has a broad range of host plants. However, the spider mite does not accept all plants to the same degree because of differences in nutritive and toxic constituents. Other factors, such as the induction of secondary metabolites, the morphology of a leaf surface and the presence of natural enemies, also play an important role in plant acceptance. We compared plants from various families in their degree of acceptance by the spider mite, to get an indication of the plant's direct defence. Glycine max (soybean), Humulus lupulus (hop), Laburnum anagyroides (golden chain) and Nicotiana tabacum (tobacco) were highly accepted by the spider mites. Different glandular hair densities among tobacco cultivars did not affect their suitability towards spider mites significantly. Solanum melalonga (eggplant), Robinia pseudo-acacia (black locust), Vigna unguiculata (cowpea) and Datura stramonium (thorn apple) were accepted by the spider mites to a lesser degree. Vitis vinifera (grapevine) was poorly accepted by the spider mite. It might be that the food quality of the leaves was not high enough to arrest the spider mites. Also, Capsicum annuum (sweet pepper) and especially Ginkgo biloba (ginkgo) were poorly accepted by the spider mite, probably because of the presence and concentration of certain of the secondary metabolites in the leaves. The spider mites accepted all the plants belonging to the Fabaceae for feeding, but those belonging to the Solanaceae showed a larger variance in spider mite acceptance varying from well accepted (tobacco) to poorly accepted (sweet pepper).
    Infochemical use by predatory mites of the cassava green mite in a multitrophic context
    Gnanvossou, D. - \ 2002
    Wageningen University. Promotor(en): M. Dicke; R. Hanna. - S.l. : S.n. - ISBN 9789058085689 - 152
    cassave - mijten - predatoren - lokstoffen - manihot esculenta - mononychellus tanajoa - gastheer parasiet relaties - voedselketens - vluchtige verbindingen - phytoseiidae - cassava - mites - phytoseiidae - predators - attractants - volatile compounds - manihot esculenta - mononychellus tanajoa - host parasite relationships - food chains
    This thesis describes research on multitrophic interactions in a system consisting of (1) cassava plants ( Manihot esculenta ), (2) three herbivorous mites, i.e. the cassava green mite Mononychellus tanajoa, the red spider mite Oligonychus gossypii and the two-spotted spider mite Tetranychus urticae and (3) two exotic predatory mites Typhlodromalus manihoti and T. aripo , in Africa. The objectives are to understand how the two exotic predators (i) exploit chemical information to locate the target prey in pure and mixed odors conditions with the alternative prey mites, (ii) perform when feeding on different prey mite species and (iii) interact with each other.

    The predatory mites, T. manihoti and T. aripo were attracted to cassava leaves infested by M. tanajoa compared with non-infested leaves, when the predators were starved for 2, 6 or 10 hours. They were not attracted to 400 female M. tanajoa removed from infested plants nor to mechanically wounded leaves. In a choice situation, T. manihoti and T. aripo preferred odors from leaves infested by M. tanajoa to odors from leaves infested by O. gossypii regardless of the ratio M. tanajoa : O. gossypii . When M. tanajoa -infested leaves and T. urticae -infested leaves were offered in a choice situation, the response of the two predator species depended on the density of T. urticae . Typhlodromalus manihoti and T. aripo were attracted to odors from cassava leaves infested with both M. tanajoa and O. gossypii or to a mixture of odors from leaves infested with M. tanajoa and odors from leaves infested with O. gossypii, when compared to odors from non-infested leaves. In contrast, mixed odors from M. tanajoa -infested leaves and T. urticae -infested leaves did not yield a preference over odors from non-infested leaves.

    Typhlodromalus manihoti and T. aripo had a higher intrinsic rate of population increase (rm) and net reproduction (Ro), and a shorter generation time and doubling time on when they were feeding on M. tanajoa than on O. gossypii or T. urticae . Prey-related odor preference matched predator performance if the key prey is compared to the two inferior prey mite species.

    Typhlodromalus aripo displayed a marked preference for odors emitted from either infested cassava apices or infested young cassava leaves over infested old cassava leaves but showed equal preference for odors from apices and young leaves both infested with M. tanajoa . Typhlodromalus manihoti did not discriminate between volatiles from the three infested cassava plant parts. This mirrors the differential distribution of the two predators on cassava plant foliage.

    Carnivorous arthropods when searching for adequate food and habitat for themselves and their progeny should in the meantime avoid becoming food for other organisms. Intraguild interactions have been investigated for the predatory mite species T. manihoti , T. aripo and the native species Euseius fustis . Typhlodromalus manihoti is able to discriminate between odors from patches with con- and heterospecific competitors and prefers to visit patches with heterospecifics. Typhlodromalus aripo preferred to move away from patches with heterospecifics or conspecifics. Euseius fustis avoided odors from patches with conspecifics as well as odors from patches with the heterospecifics T. manihoti and T. aripo .

    In conclusion, this thesis shows that the distribution and diversity of prey species, intraguild predation and competition are likely to play an important role in infochemical use by T. manihoti and T. aripo . In addition to predator-prey interactions, interactions between predators can also be considered as important factors affecting population dynamics of both prey and predators.

    Invasion of Varroa mites into honey bee brood cells
    Boot, W.J. - \ 1995
    Agricultural University. Promotor(en): M.W. Sabelis; J.C. van Lenteren. - S.l. : Boot - ISBN 9789054853480 - 119
    honingbijen - bijenziekten - plagen - dierziekten - dierpathologie - mesostigmata - dermanyssidae - phytoseiidae - honey bees - bee diseases - pests - animal diseases - animal pathology - mesostigmata - dermanyssidae - phytoseiidae

    The parasitic mite Varroa-jacobsoni is one of the most serious pests of Western honey bees, Apis mellifera. The mites parasitize adult bees, but reproduction only occurs while parasitizing on honey bee brood. Invasion into a drone or a worker cell is therefore a crucial step in the life of Varroa mites. In this thesis, individual mites, the population of mites and characteristics of honey bee brood cells have been studied in relation to invasion behaviour. In addition, a simple model has been developed to study which selective forces may have shaped the strategies used by Varroa mites with respect to the allocation of invasion and subsequent reproduction over drone and worker brood cells of the honey bee.

    Invasion behaviour of individual Varroa mites (chapter 1).
    Preceding invasion, Varroa mites are carried close to a suitable brood cell by a honey bee. The mite moves directly from the bee into the selected brood cell, crawls between the larva and the cell wall, and moves on to the bottom of the cell. At the moment of leaving the bee, the mite cannot touch the larva. It still has to cover the distance from the cell rim to the larva, which measures 4-7 mm in cells that are attractive to the mites. Thus, information to decide whether to stay on the bee or to invade a brood cell is acquired at a distance from the larva, possibly by a volatile chemical or by differences in temperature. Since invasion only occurs when a bee brings a mite close to a suitable brood cell, the chance of being carried close enough may well limit the number of mites that invade. If so, population growth of the mites is limited in turn, because the mites reproduce exclusively inside brood cells.

    Invasion of brood cells by a population of Varroa mites.
    Invasion into worker brood cells (chapter 2 & 3)
    Within a day after emergence from a brood cell, i.e. the moment when Varroa mites begin their residence period on adult bees, some mites invade a new brood cell. The percentage of mites on adult bees that invade per day depends on the number of cells suitable for invasion and on the number of bees in the colony, regardless of the time that the mites have stayed on adult bees. The more cells and the fewer bees, the higher is the percentage of mites that invade per day, as expected when invasion is limited by the chance of being carried close enough to a suitable brood cell. This can be understood as follows. Since only one or a few bees can be near a cell simultaneously, the chance of being carried close enough for invasion increases when the number of brood cells increases. In addition, in a smaller bee colony, but with the same number of brood cells, the mites are spread over a smaller number of bees. The number of bees that come close enough to a suitable cell stays the same, and therefore the mite's chance of invasion is increased.

    The percentage of mites that invade per day decreases when young open brood, still too young to be suitable for invasion by mites, is present. This decrease in invasion rate may arise because the mites prefer to be carried by young adult bees, which are likely to stay in the brood nest area. Within the brood nest area these young bees are divided over areas with brood cells that are suitable and areas that are unsuitable for invasion by mites. Hence, an increase in the amount of unsuitable open brood may keep part of the preferred young bees away from the suitable brood cells, and may thus decrease the invasion rate.

    If invasion is limited by the chance of being carried close enough to a brood cell, the spatial distribution of the mites inside the colony may affect invasion. In the areas where invasion occurs, the mite density on the bees will decrease. The mites will redistribute spatially by movement of the bees that carry them and by moving from bee to bee, but depending on the rate of this phoretic process invasion will be more or less limited. However, the rate of invasion was similar in bee colonies in which either 600 brood cells were available for mite invasion during one day or three times 200 brood cells were available during three days, whereas the colonies were comparable in all other respects. Thus, on a time scale of days the process of redistribution of mites inside the colony seems to be fast enough to prevent a significant effect of the period of brood cell availability on the rate of invasion. This is important for application of biotechnical control methods in which brood combs are introduced into the colony to trap mites. The 'trapping combs' are removed from the colony and the mites inside the cells are killed. Our results have shown that the number of cells used for trapping the mites is crucial, whereas the period during which the cells are available to the mites is of minor importance.

    Invasion into drone brood cells (chapter 4)
    Invasion by a population of mites into drone brood cells is similar to invasion into worker cells, except that invasion into &one cells is a much faster process. When invasion is compared between colonies with either exclusively worker cells or exclusively drone cells, Varroa mites invade a drone cell about 12 times more frequently than a worker cell. Hence, when both types of brood cells are available a biased distribution of 12 times more mites in drone cells than in worker cells is expected based on the differential frequency of invasion. This expected bias is larger than the bias actually found in colonies with both types of brood cells, which measures on average 8 times more mites per drone cell than per worker cell. The lower actual bias when compared to the expected one may be understood as follows. In normal honey bee colonies invasion into drone and worker cells is probably more or less segregated in time. Since the frequency of invasion is much higher per drone cell than per worker cell, the number of mites on bees will decrease much faster during periods when drone cells are abundantly present. Fewer mites will invade drone cells than expected when a constant number of mites on bees is assumed. Hence, the actual distribution over drone and worker cells may be less biased than expected from the differential frequency of invasion per cell. In addition, the biased distribution is sufficiently explained by the differential frequency of invasion per cell alone. There is no reason to believe that mites respond to the presence of nearby drone brood cells by refraining from invasion into worker brood cells, thus causing the biased distribution over drone and worker cells. Since the rate of invasion into drone brood cells is high, a trapping method using drone combs may be very effective in controlling the Varroa mite. When no other brood is present, 462 drone cells were estimated to be sufficient to trap 95% of the mites in a colony of 1 kg of bees.

    Effect of the period spent on adult bees on reproduction of the mites (chapter 5)
    No correlation has been found between the length of the period that Varroa mites stay on adult bees (1-20 days) prior to invasion and the total number of offspring per mite, the number of viable daughters per mite, the fraction of mites without offspring, and the fraction of mites that produces only male offspring. Thus, reproduction of the mites is apparently independent of the period that the mites reside on adult bees prior to invasion into brood cells.

    Mortality of mites during the period spent on adult bees (chapter 5)
    Mortality of Varroa mites, as measured by counting mites fallen on the bottom of the hive, occurs primarily right after emergence from the brood cell. When brood containing mites emerges during one day, 18% of the mites that have been present on the emerging brood is found on the bottom of the bee hive at the end of that day. Part of these mites may already have died inside the capped brood cells, and have fallen down after cleaning of cells by the bees. At the second and third day following emergence, respectively 4% and 2% of the mites on adult bees is found on the bottom, whereas from the fourth day on (up to 23 days) only 0.6% of the mites on adult bees is found on the bottom per day. Since the number of mites on the bottom of the hive will be strongly associated with the number of freshly emerged mites, counting the number of dead mites on the bottom may be a useful tool to estimate infestation levels in honey bee colonies.

    Attractiveness of brood cells to Varroa mites
    The attractive period of worker and drone brood cells (chapter 6)
    Worker brood cells are attractive to Varroa mites from 15-20 hours preceding cell capping, whereas drone cells are attractive from 40-50 hours preceding cell capping. Since the attractive period of drone cells is 2-3 times longer than that of worker cells, drone cells are consequently expected to be invaded 2-3 times more frequently. Actually, a drone cell is invaded 12 times more frequently than a worker cell. Hence, more factors must be involved in causing this difference in frequency of invasion. When the frequency of invasion is proportional to the surface of a brood cell, more mites are expected per drone cell due to its 1.7 times larger surface than a worker cell. Taken together, this would result in a 3.4-5.1 times higher frequency of invasion, which is clearly much lower than the 12 times actually found. Therefore, the higher frequency of invasion into drone cells may be attributed for an important part to differences in the information mites use to select a cell for invasion, either quantitatively or qualitatively.

    Effect of larva-cell rim distance on attractiveness of brood cells (chapter 7)
    Varroa mites are not randomly distributed over different types of cell which contain similar larvae. Per cell, more mites invade into shorter and narrower cells than control cells, whereas fewer mites invade into longer and wider cells. The period during which cells are attractive to mites varies among the different cell types, and whether in a certain type of cell more or fewer mites are found in comparison to control cells, is correlated with the length of the attractive period of that type of cell. The type of cell also affects the distance from larva to cell rim in the period preceding cell capping. When this distance is larger in comparison to control cells with larvae of the same age, the attractive period of the brood cells is shorter and vice versa. Since in all cell types the distance from larva to cell rim continuously decreases preceding cell capping, this negative correlation suggests that there is a critical larva-rim distance under which brood cells are attractive to the mites. Then, the length of the attractive period of brood cells depends on the moment this critical distance is reached. The distribution of mites over different cell types in turn results from differences in the attractive period. In normal drone and worker brood cells the critical larva-rim distance for invasion is 7-8 mm.

    Effect of methyl palmitate on attractiveness of brood cells (chapter 8)
    Since Varroa mites decide at some distance from the larva whether to stay on a bee or invade into a cell, they may well use a volatile chemical to select a brood cell. A few aliphatic esters, predominantly methyl palmitate, have been claimed to be this volatile signal for the mites for two reasons. The mites respond to the esters in an olfactometer (Le Conte et al., 1989), and the levels of the esters in worker and drone larvae may explain that drone cells are attractive during a longer period and are invaded more frequently than worker cells (Trouiller et al., 1992). However, invasion itself is unaffected by application of methyl palmitate to brood cells. In addition, analysis of headspace volatiles above attractive brood cells showed hundreds of components in the volatile blend, but in only 2 of 17 analyses a trace of methyl palmitate was found. Hence, there is no reason to believe that methyl palmitate is used as a signal for invasion by the mites.

    Reproductive strategy of Varroa mites (chapter 9)
    Since reproductive success of Varroa mites is higher in drone cells than in worker cells, the question arises why the mites do not restrict invasion to drone cells. Therefore, a simple model using population growth as a fitness measure has been developed to study under which circumstances specialization on drone brood would be a better strategy to adopt than reproduction in both types of cell. For European A.mellifera, the model suggests that if mites have to wait less than 7 days on average before they can invade a drone cell, specialization on drone brood would be a better strategy. This is close to the estimated waiting time of 6 days. Hence, small differences in reproductive success in drone and worker cells, and in the rate of mortality may determine whether specialization on drone brood will be promoted or not. In European A. mellifera colonies, Varroa mites invade both drone and worker cells, but specialization on drone brood cells seems to occur to some extent because a drone cell is more frequently invaded than a worker cell. In the parasite-host association of V. jacobsoni with African or Africanized A. mellifera or with A. cerana, the mites also invade both drone and worker cells, but the mites specialize on drone brood with respect to reproduction since a large percentage of the mites in worker brood do not reproduce. Only in the parasite-host association of Euvarroa sinhai, a mite closely resembling V . jacobsoni, and A.florea specialization is complete because these mites only invade drone brood.

    Does current knowledge of invasion behaviour help in controlling the Varroa mite?
    Our research on invasion behaviour did not result in a method in which Varroa mites are controlled using attractant or repellent chemicals. We still have to identify the signal the mite uses to invade a brood cell, although we know that mites perceive this signal at a distance from the larva and that the larva-cell rim distance affects the response of the mites to it. However, our results on invasion behaviour are useful to understand the possibilities and limitations for improvement of biotechnical control methods. We now know how many drone or worker cells are needed in a 'trapping comb' to catch a certain percentage of the mites in a colony. In theory, control methods that make use of 'trapping combs' are simple. In practice however, the methods may become complicated because application is integrated with other activities by the beekeeper like building of new colonies and swarm prevention. In addition, application of biotechnical control methods is usually labour intensive. Our results can be applied to design the simplest method that is sufficiently effective. This will remain an important application in future. Since much research is nowadays directed to breed honeybees that are less susceptable to Varroa mites (Woyke, 1989b; Büchler, 1994; Moritz, 1994), the effectiveness of control methods needed for control may decrease, which allows simplification of control methods. By combining simple 'trapping comb' methods and breeding of Varroa -less susceptable honey bees, there is a clear perspective for beekeeping without the use of acaricides to kill Varroa mites.

    Population dynamics of the thrips predators Amblyseius mckenziei and Amblyseius cucumeris (Acarina: Phytoseiidae) on sweet pepper.
    Ramakers, P.M.J. - \ 1988
    Netherlands Journal of Agricultural Science 36 (1988)3. - ISSN 0028-2928 - p. 247 - 252.
    beneficial insects - beneficial organisms - biological control - capsicum annuum - dermanyssidae - insects - invertebrates - mesostigmata - phytoseiidae - plant pests - protected cultivation - thrips - thysanoptera - neoseiulus barkeri - sweet peppers - greenhouse horticulture
    Infochemicals in tritrophic interactions : origin and function in a system consisting of predatory mites, phytophagous mites and their host plants
    Dicke, M. - \ 1988
    Agricultural University. Promotor(en): J.C. van Lenteren, co-promotor(en): M.W. Sabelis. - Wageningen : Dicke - 235
    trombidiidae - tetranychus urticae - bryobia - mesostigmata - dermanyssidae - phytoseiidae - lokstoffen - plantenplagen - gastheer parasiet relaties - parasitisme - herbivoren - vleesetende dieren - biologische bestrijding - ongewervelde dieren - nuttige organismen - trombidiidae - tetranychus urticae - bryobia - mesostigmata - dermanyssidae - phytoseiidae - attractants - plant pests - host parasite relationships - parasitism - herbivores - carnivores - biological control - invertebrates - beneficial organisms - cum laude
    What are infochemicals?

    Chemical compounds play an important role in interactions between organisms. Some of these chemicals are to the benefit (e.g. nutrients) or detriment (e.g. toxins) of an organism. Others are of benefit or detriment in an indirect way: through the behavioural response they elicit. The latter chemicals are termed infochemicals (chemicals that, in the natural context, convey information in an interaction between two individuals, evoking in the receiver a behavioural or physiological response that is adaptive to either one of the interactants or both; chapter 2). On an evolutionary time scale, the fate of an infochemical depends on selection pressures on each interactant. Selection pressure is determined by costs and benefits which result from all interactions of an organism in which the infochemical is involved. Yet, for pragmatic reasons, to analyse the function of an infochemical in the biology of an organism, a cost-benefit analysis is made for each interaction between two organisms separately. In this way the cost-benefit analysis is restricted to the smallest number of interactants possible, which ensures its simplicity. Consequently, for each interaction the infochemical is classified according to the corresponding costs and benefits for the two interactants (chapter 2; cf. Nordlund and Lewis, 1976). Moreover, classification also reflects whether the interaction under consideration is between conspecifics or between individuals of different species. This resulted in the terminology represented in Figure 1.1 and Table 1.1 (cf. chapter 2). Its structure and terms are based on those of semiochemicals. However, infochemical terminology differs from semiochemical terminology in two respects (chapter 2):

    (1) Infochemical terminology regards compounds that convey information, whereas semiochemical terminology in addition also includes toxins (Whittaker and Feeny, 1971; Nordlund and Lewis, 1976; Nordlund, 1981). In some instances toxins or nutrients may convey information. If that is the case, these toxins and nutrients are classified as infochemicals when their role as information carrier is considered. When poisonous or nutritious aspects are considered, they are not classified as infochemicals, but as toxins and nutrients respectively.

    (2) Semiochemical terminology is based on origin of the compounds, in addition to the cost-benefit analysis. Although knowledge of the origin is Important to understand the interaction between two organisms, it may be very difficult to elucidate the origin (e.g. Brand et al., 1975; chapter 4). Therefore, application of the origin criterion may lead to ambiguities. Because the cost- benefit criterion by itself is good and useful, infochemical terminology is based on that criterion alone.

    Infochemicals in tritrophic systems.

    Infochemicals play a role in interactions between consecutive trophic levels (e.g plant-herbivore, phytophagous insect- entomophagous insect; Figure 1.2) (e.g. Nordlund et al., 1981; Visser, 1986). Moreover, infochemicals may also mediate interactions between other trophic levels (e.g. plant-entomophagous insect; Figure 1.2) (Price, 1981). Therefore, to understand the selection pressure on an organism, as a result of an infochemical, all trophic levels involved should be regarded. As a consequence, investigations of infochemicals in interactions between herbivores and their predators should also regard involvement of at least the first trophic level, the plant.

    The tritrophic system of this study: predatory mites, phytophagous mites and their host plants.

    The herbivore-predator system investigated most extensively in this thesis consists of phytophagous mites and predatory mites that occur in Dutch orchards. Figure 1.3a,b depicts the two most abundant phytophagous mites that occur as pest organisms in Dutch apple orchards: the apple rust mite, Aculusschlechtendali (Nalepa), and the European red spider mite, Panonychusulmi (Koch) (Van de Vrie, 1973; Van Epenhuijsen, 1981; Gruys, 1982).

    Several species of predatory mites occur in Dutch orchards. The most abundant of these are Typhlodromuspyri Scheuten (Figure 1.3c), Amblyseiusfinlandicus (Oudemans) and A.potentillae (Garman) (McMurtry & Van de Vrie, 1973; Overmeer, 1981; Gruys, 1982). All three species feed on P.ulmi and A.schlechtendali , as well as on other food sources such as several pollens (Overmeer, 1981; Kropczynska, 1970; Overmeer, 1985).

    In this system consisting of two phytophagous prey species and three predator species (Figure 1.4a), prey preference of the predators was investigated. Optimal foraging theory predicts that natural selection favours predators preferring prey species that are most profitable in terms of reproductive success (Krebs, 1978). Reproductive success is determined, among others, by development time, oviposition rate, mortality during development and offspring quality. Each of these components can be affected by the prey species consumed. As a first step in analysing which selection pressures may have moulded prey preference of the predatory mites in the system outlined above, I have tested whether prey preference is matched by the associated reproductive success. If this most simple explanation for prey preference does not hold, other explanations should be considered (see below).

    Do infochemicals play a role in prey preference ?

    Kairomones (Table 1.1, Figure 1.1) may inform predators on presence and identity of prey (Greany and Hagen, 1981) and thereby affect foraging decisions, such as where to search, how long to search at a specific site, which prey to accept and when to disperse on air currents (chapter 3).
    Investigation of the response to kairomones may therefore yield information on prey preference. However, the conclusion on prey preference must be restricted to the foraging phase that was studied. Relative costs involved in finding individuals of each prey species might differ for different foraging phases. Therefore, to obtain a comprehensive view of prey preference, several foraging phases should be investigated. Such analyses should be carried out independently to obtain complementary conclusions. In this study, prey preference was determined in three independent analyses.
    Two laboratory analyses were carried out:
    - Analysis of response towards volatile kairomones. This investigation regards decisions of the predators when prey individuals are not contacted, as is the situation after termination of aerial dispersal or after eradication of a prey patch.
    - Analysis of predation rates at different prey supplies. This relates to acceptance/rejection decisions during contacts with prey items.
    To complement the prey preference analyses carried out in the laboratory, an investigation was made under field conditions: - This was done by determination of diet composition by means of electrophoretic analysis of gut contents of field-collected predators.

    Spider-mite kairomones in a tritrophic context.

    Predatory mites distinguish plants infested by spider mites from clean plants by a volatile kairomone (e.g. Sabelis & Van de Baan, 1983). This kairomone seems to be a product of the interaction between plant and spider mites: after removal of spider mites from an infested plant, the plant remains attractive to the predators during several hours, whereas the mites alone do not remain attractive (Sabelis & Van de Baan, 1983; Sabelis et al., 1984a). Current data on spider mite - predatory mite interactions do not explain the role of this infochemical in the biology of the spider mites (cf. chapter 3 for a review). It may, for instance, be an inevitable byproduct of damage inflicted on the plant by the spider mite, and/or have an indispensable function in the biology of the spider mite. Moreover, the plant may be involved in production of the infochemical. To elucidate the role of this volatile infochemical, its effects in interactions between plant and spider mite, between plant and predatory mite and between spider mites of one species should be investigated. Before this can be done, chemical identification of the infochemical is a necessary first step.

    These investigations were made for a tritrophic system consisting of Lima bean plants, the two-spotted spider mite, Tetranychusurticae Koch and the predatory mite Phytoseiuluspersimilis Athias-Henriot (Figure 1.4b). This system was chosen for practical reasons. The plant and phytophagous mite can be reared throughout the year and therefore, this system is much more suitable to develop a method for the chemical analysis of spider-mite kairomones than a system in which the plant is a perennial.

    Origin and function of T.urticae kairomone in a tritrophic system.

    Two-spotted spider mites distinguish between a clean plant and a plant that is infested by conspecifics on the basis of a volatile infochemical (chapter 4). The spider mites move away from heavily infested leaves. This response is advantageous to spider mites on the infested leaf as well as to spider mites that avoid settling on these leaves: increased competition for food is avoided, cf. Wrensch and Young (1978). In addition, the spider mite that disperses thus avoids settling on a spot that has an increased risk of being detected by predatory mites (Sabelis and Van de Baan, 1983). Therefore, the infochemical in this interaction between conspecific spider mites is called a (+,+)dispersing pheromone. Biological evidence suggests that this pheromone is (at least partly) identical to the volatile kairomone to which predatory mites respond (chapter 4).

    Volatiles emitted from plants infested by T.urticae were identified and subsequent behavioural analyses resulted in identification of four kairomone components that attract the predatory mite P.persimilis : linalool (3,7-dimethyl-1,6-octadiene- 3-ol), methyl salicylate, ( E )-β-ocimene (3,7-dimethyl-1,3( E ),6- octatriene) and 4,8-dimethyl-1,3( E ),7-nonatriene. The structure of these compounds is shown in Figure 1.5. At least two of these (linalool and methyl salicylate) are also components of a kairomone in the interaction between T.urticae and A.potentillae (when reared on V.faba pollen; see below) (chapter 4). Literature data on the behavioural response of T.urticae indicate that one of these kairomone components (linalool) is also a component of the (+,+)dispersing pheromone (Dabrowski and Rodriguez, 1971).

    All identified kairomone components are well-known in the plant kingdom. This suggests that the plant is involved in production of the infochemical, but it is no proof. It may for Instance be that spider-mite enzymes injected into the plant break down a plant compound. Investigation of e.g. site and moment of production and possible storage of precursors are needed as a next step to elucidate the role of the plant in kairomone production. However, suppose that it is the spider mite who produces the infochemical to serve as a dispersing pheromone. Then, it is not clear why this pheromone should necessarily consist of volatiles. As a result of the production of volatiles the spider mites incur more risks of being detected by predators than by production of non-volatile chemicals. Detection by predators inevitably leads to local extermination of spider mites (Sabelis and Van der Meer, 1986). For this reason it seems more likely that the volatiles are plant produced and that the spider mite makes the best of a bad job by using them as information to decide where not to colonize. To understand the evolution of plant-produced volatiles after herbivore attack, it is crucial to assess how they are produced, how much it costs to produce them and what the benefits are in terms of a lowered probability of herbivore attack.

    Involvement of volatile kairomones in prey preference of predatory mites.

    The response of T.pyri and A.potentillae to volatile kairomones is dependent on the diet of the predators. When reared on a carotenoid-poor diet these predators respond to the kairomones of more prey species than when reared on a carotenoid-rich diet (chapters 6, 7 and 8). Carotenoids are indispensable to A.potentillae because of their function in diapause induction (Overmeer, 1985a). The function of these nutrients to T.pyri remains unknown (chapter 8). All prey species to whose kairomones carotenoid-deficient A.potentillae and T.pyri respond can relieve the lack of carotenoids. Carotenoid-containing A.potentillae and T. pyri only respond to the P.ulmi kairomone. The above observations were made for predators that were starved for 20 h. Longer starvation of predators reared on a carotenoid-rich diet also enlarges the number of prey species responded to. Investigations of the response to volatile kairomones indicates that A.potentillae and T.pyri (whether carotenoids are available or not) prefer P.ulmi to A.schlechtendali (chapters 6, 7 and 8) and that A.finlandicus has a reverse preference (chapter 11).

    This corresponds to conclusions from predation experiments performed at different composition of prey supply (chapters 9 and 11). The observed predation rates when mixed prey supplies were offered, were compared with a model provided with parameters estimated from experiments with each of both prey species alone. Amblyseiuspotentillae and T.pyri fed more on P.ulmi and A.finlandicus fed more on A.schlechtendali than was predicted by the model. This difference between observed and predicted predation rates cannot be explained by a change in behaviour of the prey species as a result of being together, nor by a change in walking behaviour of the predator. Therefore, these data indicate that A. potentillae and T.pyri prefer P.ulmi and that A.finlandicus prefers A.schlechtendali , in terms of a change in acceptance/rejection ratio ('success ratio').

    Analysis of prey preference under field conditions showed that most T.pyri collected from apple leaves that widely varied in P.ulmi : A.schlechtendali numbers contained P.ulmi esterase, whereas A.schlechtendali esterase was present in a minor fraction of predators (chapter 10). Rust-mite esterase and P.ulmi esterase were found equally frequent in A.finlandicus . The data for A.finlandicus , obtained over a narrower range of prey-number ratios than for T.pyri , do not allow a definite conclusion on prey preference. However, they certainly do not cause rejection of the conclusion on prey preference as obtained in the laboratory analyses (chapter 11). No field data are available for A.potentillae .
    Because the conclusions on prey preference as determined in these independent analyses are consistent for each predator species, the inference on prey preference is firmly established.

    Prey preference and reproductive success of predatory mites in an orchard system with two species of phytophagous prey mites.

    Analysis of reproductive success of these three predator species, when feeding on either P.ulmi or A.schlechtendali , indicates that A.finlandicus selects the best prey species in terms of reproductive success. This predator species suffers high larval mortality on P.ulmi , but not on A.schlechtendali . This results in a much higher intrinsic rate of population increase when feeding on apple rust mites (chapter 12).

    Amblyseiuspotentillae and T.pyri would also do better by feeding preferentially on A.schlechtendali : development times when feeding on this prey species are shorter than when feeding on P.ulmi , whereas these prey species do not differentially affect mortality or oviposition rate (chapter 12). For A.potentillae this may not be the case at the end of the season because P.ulmi is a better prey species in terms of diapause induction. Thus, on the basis of current data, optimal prey-choice theory cannot satisfactorily predict actual prey peference of A.potentillae and T.pyri . Future investigations should concentrate on e.g. (1) possible effect of competition between prey species on prey availability, (2) possible effect of competition between predator species on prey availability, and (3) possible shift in prey preference during the season.

    Phytoseiid mites on tree crops, ornamental and wild plants in the Netherlands
    Vrie, M. van de - \ 1972
    Wageningen : [s.n.] (Mededeling / Instituut voor plantenziektenkundig onderzoek no. 591) - 8
    plantenplagen - vruchtbomen - boomgaarden - mesostigmata - dermanyssidae - phytoseiidae - nederland - plant pests - fruit trees - orchards - mesostigmata - dermanyssidae - phytoseiidae - netherlands
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